class Solution(object):
    def titleToNumber(self, s):
        """
        :type s: str
        :rtype: int
        """
        tn_dict = {
            'A':1, 'B':2, 'C':3, 'D':4, 'E':5, 'F':6, 'G':7, 'H':8, 'I':9, 'J':10,
            'K':11, 'L':12, 'M':13, 'N':14, 'O':15, 'P':16, 'Q':17, 'R':18, 'S':19, 
            'T':20, 'U':21, 'V':22, 'W':23, 'X':24, 'Y':25, 'Z':26
        }
        sum = 0
        for i in range(len(s)):
            n = len(s) - 1 - i
            sum += tn_dict[s[n]] * 26 ** i
        return sum
